Genetic Structure Of Chinese Geographical Populations Of Cotesia Vestalis(Haliday)(Hymenoptera: Braconidae)

The population genetic structure in of Cotesia vestalis across China was investigated based on mitochondrial genes and microsatellite loci by analyzing the diversity, population structure and demographic history. The factors influencing the genetic structure of C. vestalis was discussed. The main results are as follows:(1) Two mitochondrial genes(cox1 and cytb) and 17 microsatellite loci in 158 individuals from the 12 C. vestalis populations(covering the major regions in China) were examined. There are 12 haplotypes from the combined genes of cox1 and cytb, 7 haplotypes from cox1 and 8 haplotypes from cytb. Totally 242 alleles in the 17 microsatellite loci and each population had more than 50 alleles in the 17 microsatellite loci.(2) C. vestalis was obviously differentiated in China based on the analyses of mt DNA and microsatellite loci. The value of population genetic differentiation(Fst) based on the combined mitochondrial genes was ranged from –0.074 to 0.917 with 42 pairwise of populations were highly significant in 66 population pairs; The value of Fst based on the 17 microsatellite loci was ranged from –0.006 to 0.028 with 50 pairs of population were highly significant in 66 population pairs.The value of nucleotide diversity and haplotype diversity from YNKM population was higher than those of other populations. The value of mean number of allele, observed heterozygosity, expected heterozygosity and allelic richness was ranged from 4.765 to 8.000, 0.590 to 0.783, 0.656 to 0.788 and 3.067 to 3.821, respectively.(3) Based on NJ-tree constructed from mt DNA and microsatellite loci and the parsimony network of the 12 haplotypes from the combined mitochondrial genes, populations of C. vestalis in China were divided into three clades associated with geographical locality, that is SC(southwestern China), MC(middle region of China), NC(northern and northeastern China) clades. Beyond the three clades, the YNKM(Kunming population from Yunyan Province) in SC clade showed highly differentiation from other populations, and the XJAL(A Laer population from Xinjiang Province), XJWS(Wulumuqi population from Xinjiang Province), HJHB(Ha Erbin population from Hei Longjiang Province) and JLCC(Changchun population from Jilin Province) populations which from NC clade also showed highly differentiation from the MC clade. The divergent time between SC and NC, MC clade was 0.41 million years ago(mya), within SC clades was 0.02 mya, and between NC and MC clade was 0.09 mya.(4) The results of Mantel-test based on mt DNA and microsatellite loci indicated that there is an isolation by distance and a relationship between genetic distance and geographical distance in populations of C. vestalis(mt DNA: r = 0.595; P = 0.001; SSR: r = 0.651; P = 0.012).The population genetic structure was analyzed using software BAPS, GENELAND and STRUCTURE based on mt DNA or microsatellite loci. Three clades were identified by using BAPS based on mt DNA and microsatellite loci. Based on mt DNA the 12 populations were divided into 4 clades(XJAL and XJWS were divided into two clades) by using GENELAND, but 3 clades based on microsatellite loci. Based on microsatellite loci, 3 clades were divided by using STRUCTURE. Although there are differences among these analyses, the results indicated that there were 3 clades(SC, MC and NC) in the 12 populations of C. vestalis.(5) The analysis of gene flow based on the 3 clades(SC, MC and NC) showed that the value of gene flow of C. vestalis in China were very low. It indicated that the low gene flow can lead genetic differentiation among different populations and an isolation between the 3 clades which be caused by geographical obstructs and its feature of non-migration.(6) The results of neutrality tests based on the combined mitochondrial genes showed that the value of Tajima's D from 7 populations of HJHB, SXYL, GXNN, JLCC, XJWS, XJAL and YNKM were ranged from-2.333 to 2.611, which were significantly deviated from zero.The mismatch distribution of the three clades of C. vestalis based on the two combined mitochondrial genes indicated that the value of observation was very similar to the simulation, it was concluded that the 3 clades were both under the hypothesis of population expansion(G1: P = 0.250; G2: P = 0.810; G3: P = 0.980; G1 = SC, G2 = MC, G3 = NC).